What is goku fused with gohan?

In Dragon Ball Z, Goku and Gohan never really fused into one character. They did perform the "Father-Son Kamehameha" technique in the Cell Games Saga where they combined their powers, but they did not merge into a single entity.

However, in Dragon Ball Fusions, a video game for the Nintendo 3DS, there is a fusion called "Goghan" which is a combination of Goku and Gohan. The character is a physical representation of what their combined powers would look like, essentially blending Goku's fighting prowess with Gohan's intelligence and potential.

Overall, while Goku and Gohan have worked together and combined their powers in various ways throughout the Dragon Ball franchise, a true fusion where they become one character is not canon to the series.